How is the weight of a flange calculated?

Sometimes some customers only provide the size of the required flange but don't provide the single piece weight of the flange，then how to calculate the single piece weight of the flange?
The engineer of Shandong AiGuo Forging Co., Ltd. will explain to you:

Flange: OD * OD - ID * ID - pore diameter * number of holes)* Thickness *0.617*0.00001 (it is better to provide the pore diameter of bolt holes and the number of holes of bolt holes)

Elbow: Caliber - thickness) * Thickness *0.02466* Length = weight (kg)